1. Field of the Invention
This invention relates to safety, operating cost, planned maintenance and/or repair of vehicles using pneumatic tires. The present invention more particularly relates to systems and devices for sensing air pressure in pneumatic tires of a vehicle, and to tire pressure monitors of the type which are capable of sensing incorrect pressure and alerting the operator of a vehicle of incorrect tire pressure while the vehicle is being operated.
2. Description of Prior Art
A past art search was conducted at the U.S. Patent and Trademark Office to examine known tire pressure monitors. The following U.S. Patents disclose tire pressure monitors considered pertinent to my invention:
A patent issued to T. A. Gee et al in Jan. 1982, U.S. Pat. No. 4,311,985, discloses a tire pressure monitor and de-energization circuit therefore. The Gee et al patent discloses a device which is activated by a centrifugal switch when the vehicle moves and then continuously monitors the tire air pressure. The Gee et al device further utilizes a receiver in the passenger compartment which receives pulsed signals from a transmitter, and by counting the pulsed signal determines the tire pressure condition. The Gee et al device samples the tire pressure only when the pressure exceeds a preset value and notes the condition to the operator. False alarms and radio interference do not appear to be adequately addressed, and consequently false signals are seen to be a likely problem in the Gee et al device.
A patent issued to D. M. Brown in Dec. 1990, U.S. Pat. No. 4,978,941, discloses a low tire pressure detector. This device is hub mounted and uses a transmitter/receiver to send a low pressure alert signal to the operator. The device senses a low pressure signal from a low pressure switch and transmits this signal to the operator. The operator may then stop the vehicle and by inspecting each individual wheel, determine which tire has the under pressure condition. An indicator is located on each wheel to assist the operator in determining the low pressure tire. Isolation from other vehicles to reduce the number of false signals is obtained only partially through delay logic, and consequently, false alarms with this device are seen to be a likely relatively frequent problem.
A patent issued to A. N. Strickland et al in Nov. 1958, U.S. Pat. No. 2,860,321, discloses a tire alarm system, which senses both high and low tire pressure. The Strickland et al system uses pressure sensors and radio transmitters and receivers to notify the operator of a high or low pressure condition. The method of signaling is by transmitting a given frequency for each tire. Interference between vehicles equipped with this device does not appear to be adequately addressed, and consequently, false alarms are also seen to be a likely problem with this system.
A patent issued to C. F. Morrison Jr. et al in Jan. 1988, U.S. Pat. No. 4,717,905 discloses a warning system for tire air pressure including means for remotely energizing a sensing device. Several means are discussed including using RF transmission, through a receiving antenna and capacitors which will store the received power and supply this power to the pressure sensors and transmitter which transmits to the receiver the status of the tire. The system appears to use a pressure transducer to transmit the actual tire pressure when activated. The data is transmitted at a different frequency for each tire or set of tires. Also described is the use of tuned antennas which are affected by tire pressure which results in changed antenna impedance which in turn indicates a tire pressure. Calibration of the antennas would give information on pressure changes. The devices described in this patent use radio frequency devices and antenna responses primarily to detect tire anomalies.
A patent issued to E. J. Nagy in Aug. 1981, U.S. Pat. No. 4,286,253, discloses a tire pressure sensing and alarm system. The Nagy device uses a radio transmitter and radio receiver activated by a low pressure switch which causes a transmitter to transmit to a receiver which then presents an audio or visual display to the operator. The operator may then stop the vehicle and inspect each wheel to determine the particular wheel on which the low pressure tire is located. Nagy does not appear to address false signals or radio interference.
The tire pressure monitors of the prior art are similar, and to the present invention for that matter, typically including pressure sensors or pressure transducers, radio or infrared transmitters and receivers, and displays or alarms to alert the vehicle operator of a problem in tire pressure. Each of the prior art tire pressure monitors seem to have one or more undesirable attributes which may explain the apparent general absence of the use of such devices, and indicate there exists a need for an improved tire pressure monitor or monitoring system. Some of the problems found in the prior art devices include the monitoring of low tire pressure only; the lack of adequate structuring to safe guard against internally generated false signals and false signals caused by other vehicles having similar tire pressure monitors; the problem of requiring visual inspection of each wheel to determine which tire has an incorrect air pressure; and excessive use of battery power.